I have a 98 ranger with 137000 miles on it (4x4 4.0 auto xlt). The valvetrain was making so much noise it sounded like a diesel. I tried going to 20-50 weight oil and even put in some Lucas oil stabilizer in hopes that the noise would get quieter but it only made it worse. I went back to 30 weight the next oil change and the noise persisted. The night that I went back to 30 weight I was reading about the poor oil flow to the heads and figured that I might have some sludge or something inhibiting the oil flow, so the next morning I drained my oil and put in 5-20 weight with a can of seafoam. I drove it for about 500 miles with the seafoam and noticed that the noise was gone, I figured that whatever was constricting the oil flow had been cleaned out so I changed the filter and replaced the oil with 30 weight again, the noise came back immediately. So I drained the oil and removed the filter. This time I put in a K&N oil filter and Mobil1 synthetic 0w-20 weight oil. Within 20 miles the noise went away and has not returned. I am sure that this will not work for everyone but it might be worth a try if y'all are looking at an expensive resolution for this issue. If you are reading this you more than likely own a ranger and I want to say thank you for buying an American truck. God Bless America!!!

 

Is this noise at idle or higher throttle?

 

how do you run seafoam?

 

the noise was from idle to about 1900rpm

 

I just ran the seafoam in the crankcase with about 4.5 quarts of oil (5w-20) for 500 miles

 

Are you sure you are not mistaking the noise piston slap which is a common issue on '98 4.0L?

 

according to my stethescope it was all valvetrain noise, the bottom end is solid.

 

its not poor oil flow to the heads its poor oil flow in the heads, and its not sludge in there its just the wear and tear to the valvetrain over time due to lack of oil flow in the heads that causes it to sound like a coffee can full of marbles. low mileage 4.0's dont make the sound but they do as they get older. mine did it, glad to be rid of that motor and have the sohc within the years that the chain error was corrected.

 

Definitely Piston Slap not valvetrain slop. There are a few threads about it on RPS. It is known as "Marbling". Some of the 4.0L OHV motors particulary the 1998 have offset wrist pins which cause the piston to wobble at low rpm and load. It is not harmful just annoying. Mileage might have something to do with it. It usually occurs after the truck has sat dormant for a while or after an oil change. If you want to avoid this when you change your oil, change it as fast as you can and put in the drain plug as soon as the oil flow starts dripping. Heavier weight oil or Lucas Oil stabilizer will not help, you want a thinner oil with better flow. To minimize the marbling use a synthetic oil and a higher flow oil filter. The Triton V10 was also notorious for this problem.

My truck is currently not doing this but I have had issues with it in the past. However anytime I adjust the Idle below 600 RPM it marbles like crazy and sounds worse than a 7.3L diesel.

 

that is true lol my mistake for using that to describe the noise, my old 4.0 did that. although its annoying that motor will just run forever.

 

my valves make noise and my truck has 275k on i just keep the oil changed and take care of it